This invention relates to a system for removing particles from exhaust produced by internal combustion engines, such as diesel engines.
Exhaust produced by diesel engines has a relatively high content of polluting particles composed of carbon, unburned fuel, and partially burned fuel. Filters disposed in engine exhaust systems are conventionally used to remove the particles from the exhaust. In this case, burners positioned in the exhaust systems upstream of the filters are often employed to burn off the particles deposited on the filters in order to unclog and rejuvenate the filters.
Japanese patent publication No. 56-115809 discloses such a particle removing system. In this system, the pressure across the filter is monitored as an indication of the degree of clogging of the filter When this pressure rises to a preset level, the burner is activated to unclog the filter. The pressure across the filter, however, inaccurately represents the degree of clogging of the filter for the following reason: this pressure depends not only on the degree of clogging of the filter but also on the rate of exhaust flow. This inaccuracy in the recognized degree of clogging of the filter could allow clogging to an acceptable level or wasteful overuse of the burner.